PROJECT SUMMARY Pain is the most common and most costly neurological disorder in HIV-1/AIDS patients, yet current pain treatment provides only symptomatic management that is often ineffective. Lack of deep, mechanistic understanding of the underlying mechanism of HIV-associated pain has significantly impeded the development of needed effective, rationale-based approaches for pain control in HIV patients. Emerging evidence suggests a crucial role for neuron-astrocyte interactions in the spinal dorsal horn (SDH; the pain processing center in the spinal cord) in the pathogenesis of HIV-associated pain. However, the mechanism that mediates these intercellular interactions is largely unknown. Our work prior and preliminary studies suggest that gp120 elicits exosome-based signals to mediate bidirectional neuron-astrocyte communication in the SDH. Importantly, the exosome pathway is up-regulated in the SDH of the HIV patients with pathological pain. Pharmacological inhibition of exosome secretion in the SDH blocks the expression of gp120-induced pain. We propose that exosome-mediated neuron-astrocyte interactions play a critical role in gp120-induced pain pathogenesis. Specifically, we hypothesize that gp120 stimulates exosome-based secretion of Wnt signaling protein from SDH neurons, which then stimulates astrocytes to release exosomes that in return feedback to SDH pain processing neurons to promote central sensitization. We will use an interdisciplinary approach of conditional knockout, mosaic analysis, patch clamp recording and behavioral analysis to test this hypothesis. The mechanistic insights gained from this project will facilitate the development of novel therapies for HIV- associated pain targeting this underlying exosome-mediated pathogenic process.